Turbochargers which utilize the energy of the exhaust gas from an internal combustion engine to generate high-speed rotation of a turbine, using that rotational force to drive a centrifugal compressor, and then feeding the resulting compressed air into the engine to enhance the thermal efficiency as an internal combustion engine are already known.
A turbocharger fitted to an internal combustion engine is provided with a nozzle mechanism or valve mechanism that diverts a portion of the exhaust gas and adjusts the inflow into the turbine.
The mechanism components such as bearings and bushes built into the turbocharger are continuously exposed to the high-temperature corrosive exhaust gas discharged from the engine, and are also moveable components that require excellent sliding characteristics.
Conventionally, heat-resistant components of wrought materials or sintered materials formed from high-Cr steel have been used for these types of sliding components exposed to high-temperature corrosive exhaust gases.
One example of a conventionally known sintered alloy for use in heat-resistant components is a sintered alloy having an overall composition containing, in mass % values, Cr: 11.75 to 39.98%, Ni: 5.58 to 24.98%, Si: 0.16 to 2.54%, P: 0.1 to 1.5% and C: 0.58 to 3.62%, with the remainder being Fe and unavoidable impurities, and having a metal structure that includes a phase A containing precipitated metal carbides with an average particle size of 10 to 50 μm and a phase B containing precipitated metallic carbides with an average particle size of 10 μm or less which are distributed in a patchy manner, wherein the average particle size DA of the precipitated metallic carbides in the phase A and the average particle size DB of the precipitated metallic carbides in the phase B satisfy DA>DB (see Japanese Unexamined Patent Application, First Publication No. 2013-057094).